The number of possible natural oscillations of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are (velocity of sound `=340ms^(-1)`).

Options

A. 7
B. 6
C. 4
D. 5

Answer

B

Explanation

The fundamental frequency
`n = v/(4l) = (340 xx 100)/(4 xx 85) = 100 ` Hz
and as only odd harmonics are heard in a pipe closed at one end, the possible frequencies are 100, 300, 500 , 700, 900, 1100, 1300, etc.
` :. ` The frequencies below 1250 are
` 100, 300, 500, 700, 900 " and " 1100`.
Thus the number of possible natural oscillations is 6.